The CRA statute and regulation are both silent on this, so you may change your AA at any time. I don't think it is a good idea to do that on your own though. I'd get at least your supervisor's ok, if not the board's, but that isn't required either.
BTW, want to see your examiner become short of breath and clutch his/her chest? Just wait for them to get near the end of a CRA exam, particularly a large bank CRA exam, and just mention that, oh, by the way, did we tell you we changed our AA?